Vehicle impact attenuators are installed in places where vehicle collisions tend to occur, such as the ends of median strips, road forks, and the ends of branch points for tollgates, in order to immediately stop a colliding vehicle and mitigate the impact applied to the vehicle, thereby preventing secondary accidents and reducing damage to the vehicle and its occupants.
Guard fences, such as steel guardrails or guard cables, can be described as vehicle impact attenuators. However, with these devices, colliding vehicles still receive a large impact, and the damage to the occupants and vehicles cannot be effectively inhibited. Further, these devices are likely to greatly damage the colliding vehicles and the scattered fragments are liable to cause secondary accidents.
Other vehicle impact attenuators include water-filled container-type impact attenuators. However, this type of devices also pose a problem in that a vehicle receives a large impact when it collides with them while traveling at a high speed. Further, containers knocked over by a vehicle may scatter on the road, or a colliding vehicle may not be decelerated even after knocking down the containers and may jump over the base of the containers into the opposite lane, causing secondary accidents.
In view of such problems, the present inventors conducted extensive research and proposed vehicle impact attenuators that comprise a shock absorber and a support fixed on the ground so as to support the shock absorber, wherein the support is released from the ground and made slidably movable when a load exceeding a set value is applied by a vehicle collision (Japanese Unexamined Patent Publication No. 2001-159107, hereinafter “Publication 1”, and Japanese Unexamined Patent Publication No. 2003-64629, hereinafter “Publication 2”). The proposed devices make it possible to effectively absorb the impact, immediately stop the vehicle, and prevent the vehicle from receiving an impact load exceeding a set value.
However, since vehicle impact attenuators are generally installed in narrow places with limited space, such as the ends of median strips, the devices must be miniaturized or improved in impact load absorbing capacity per installation space, so as to allow a smooth traffic flow and make the devices installable in more places. Moreover, the installation cost of vehicle impact attenuators must be reduced in order to make the devices installable in many places.